Irradiation with UVB at levels lower than required for the formation of tumors results in ultrastructural changes in the dermal layer of skin. Using two photon excitation microscopy of elastin and collagen autofluorescence we have investigated these changes in hairless mice exposed to controlled levels of UVB irradiation and found large increases in elastin at depths of 100 to 200 microns in the dermis after a 5 Joule dose of UVB radiation. Measurements using biochemical isolation and quantification have produced similar results, but the location and structure of the new synthesized elastin fibers was previously unknown.